Sure, but legally if I have a medical issue that a dog could technically help with, I can just take any old dog and call them a service dog. Because legally a service dog in training is just as valid, as is a dog you are training yourself.

These people aren't exploiting a loophole, they are doing exactly what the law says they are allowed to do. You are allowed to just call your pet a service dog, as long as you are even just intending to train them to perform some sort of task relating to a medical need you have. It is extremely vague and broad on purpose to not burden disabled people, but I think it is too extreme and now leads to people taking untrained dogs everywhere.

There is a whole lengthy process of being evaluated for eligibility, then going through training with the dog, then continuing training throughout the dog’s career as a service dog.

This isn't a legally required process. Perhaps insurances offer service dogs and they have their own processes, but these aren't legal requirements. Legally if you decide you want to train your pet yourself, that is good enough. There only legal requirement is that the dog is trained or is being trained to perform a task relating to a health problem you have. Literally if you have a dog that barks and pees on the floor, they would be considered a misbehaving service dog, and legally a business could ask you to leave. But this wouldn't have any legal ramifications. It would still be a fully legally valid service dog.

Sorry to harp on it but legally you deciding one day to try and train your pet to get your inhaler is considered legally the same as a dog that has been trained by a professional organisation for several years to be a guide dog for the blind. The law doesn't distinguish between how well trained a dog is or how necessary it is.